Those doing the hiring really do read those cover letters. They have to. Otherwise, there would be nothing to go on to make the first cut: selecting 10 or 20 to interview for jobs and contract assignments.
Yet, burned-out job hunters frequently treat creating cover letters as if it were a numbers game. They click hundreds or thousands annually into cyberspace, none presenting them in a way that gives them an edge. Most, if not all the cover letters, resemble each other.
When they get no response they blame the economy, their age, the fact that they had been laid off from their last job or even the city they live in (too far from Manhattan).
The smarter game plan would be to frame each cover letter as the unique opportunity it is to connect with that human being in charge of hiring.
It's simple respect to show you took time with the letter. That begins with reading the help-wanted carefully. From the tone, language and even length, you can get clues about the organizational culture and what they are looking for in a candidate. Based on that, you plan a strategy how to describe your track record and how that equips you to exceed what is needed.
Sure, you can copy and paste from a general pattern letter. However, it's in your self-interest to custom-make short paragraphs that kill it. One might demonstrate your deep understanding of cloud computing, which is among their services. Another might highlight your ideas for marketing, without seeming too aggressive. A third might contain links to articles you published about the potential of an emerging technology.
Depending on the field you are in, inserting a graphic could make you stand out. For instance, if you are in operations, you might design a flow chart. If in social media, an infographic. If in design, your own logo.